Growth method of nitride semiconductor layer and light emitting device using the growth method

ABSTRACT

Growing a first nitride semiconductor layer on an Al x Ga y In I-x-y N (0&lt;x&lt;1, 0&lt;y&lt;1, 0&lt;x+y&lt;1) layer, a second step for reducing the thickness of the first nitride semiconductor layer by growth interruption and, growing a second nitride semiconductor layer having a band gap energy higher than that of the first nitride semiconductor layer on the first nitride semiconductor layer with the reduced thickness and a light emitting device using the growth method.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a U.S. Divisional application of U.S. National Phaseapplication Ser. No. 10/596,126 filed May 31, 2006, which claims thebenefit of priority of International Application No. PCT/KR2004/002688filed Oct. 20, 2004, which claims the benefit of Korean PatentApplication No. 10-2004-0063722 filed Aug. 13, 2004. The disclosures ofU.S. application Ser. No. 10/596,126, and International Application PCTApplication No. PCT/KR2004/002688, are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to development of a UV light source usingnitride semiconductors, and more particularly, it relates to developmentof a nitride semiconductor light emitting device having a high lightemission efficiency and a single light emission peak by using an In-richInGaN quantum well layer with a thin thickness, instead of theconventional Ga-rich InGaN quantum well layer, as an active layer.

BACKGROUND ART

A Ga-rich InGaN quantum well layer comprising 10% or less of InN ismainly used to form a UV light source using nitride semiconductors. Itis known that as the light emission wavelength is reduced, the lightemission efficiency is lowered.

Generally, in case of a green or blue light source in the visible lightrange using nitride semiconductors, it is possible to obtain a highlight emission efficiency in spite of a high defect density in a thinlayer due to the absence of a proper substrate. This is because of theformation of a local carrier energy level caused by phase separation andcomposition nonuniformity of InN in the InGaN quantum well layer. It isknown that this effect can be increased as the compositional rate of InNis increased.

However, in case of a UV light source, the InN composition in the InGaNquantum well layer is smaller than that in the visible light source, thelocal carrier energy level is rarely formed and thereby, the lightemission efficiency is lowered. Also, as compared to the green or bluelight source, the difference of energy level between an InGaN quantumwell layer and a capping layer (or barrier layer) is small and thereby,the carrier confinement effect is reduced, causing a decrease in thelight emission efficiency.

For these reasons, it is impossible to have a high light emissionefficiency in the conventional UV light source using a Ga-rich InGaNquantum well layer with an InN composition of 10% or less.

DISCLOSURE Technical Problem

Accordingly, the present invention has been made to solve theabove-mentioned problems occurring in the prior art, and it is an objectof the present invention to provide a method for producing a highefficiency light emitting device having a emission wavelength in the UVrange using an In-rich InGaN quantum well layer with a thin thickness asan active layer.

Also, it is another object of the present invention to provide a methodfor growing a quantum well layer comprising an In-rich region and aregion with an In compositional grading (or In composition gradient) anda nitride semiconductor light emitting device using the same. In orderto provide a light emitting device comprising an active layer having adesired wavelength, the wavelength of the active layer should becontrollable or expectable. Through experiment and theoreticalcalculation, the present inventors have found that the PL(Photoluminescence) peak of an In-rich InGaN layer which has undergonesufficient growth interruption can be moved to the UV region. Based onthe findings, the present invention is to provide a nitridesemiconductor light emitting device comprising an In-rich InGaN quantumwell layer with a controllable emission wavelength.

Technical Solution

To accomplish the above objects, according to the present invention,there is provided a growth method of nitride semiconductor layercomprising a first step for growing a first nitride semiconductor layeron an Al_(x)Ga_(y)In_(1-x-y)N (0≦x≦1, 0<y≦1, 0<x+y≦1) layer, a secondstep for reducing the thickness of the first nitride semiconductor layerby growth interruption and a third step for growing a second nitridesemiconductor layer having a band gap energy higher than that of thefirst nitride semiconductor layer on the first nitride semiconductorlayer with the reduced thickness.

Here, the Al_(x)Ga_(y)In_(1-x-y)N (0≦x≦1, 0<y≦1, 0<x+y≦1) layer, thefirst nitride semiconductor layer, and the second nitride semiconductorlayer may be doped with p-type or n-type impurities and theAl_(x)Ga_(y)In_(1-x-y)N (0≦x≦1, 0<y≦1, 0<x+y≦1) layer and the secondnitride semiconductor layer are formed of preferably GaN.

Also, according to the present invention, there is provided a nitridesemiconductor light emitting device comprising a substrate, at least onenitride semiconductor layer grown on the substrate and including an toplayer of Al_(x)Ga_(y)In_(1-x-y)N (0≦x≦1, 0<y≦1, 0<x+y≦1), a quantum welllayer grown on the top layer of Al_(x)Ga_(y)In_(1-x-y)N (0≦x≦1, 0<y≦1,0<x+y≦1), and an additional nitride semiconductor layer grown on thequantum well layer and having a band gap energy higher than that of thequantum well layer, in which the quantum well layer comprises an In-richregion, a first compositional grading region with In content increasingbetween the top layer of Al_(x)Ga_(y)In_(1-x-y)N (0≦x≦1, 0<y≦1, 0<x+y≦1)and the In-rich region, and a second compositional grading region withIn content decreasing between the In-rich region and the additionalnitride semiconductor layer.

Here, the top layer of Al_(x)Ga_(y)In_(1-x-y)N (0≦x≦1, 0<y≦1, 0<x+y≦1),the quantum well layer and the additional nitride semiconductor layermay be doped with p-type or n-type impurities.

Also, according to the present invention, there is provided a nitridesemiconductor light emitting device having a quantum well layer with athickness of 2 nm or less, in which the two-dimensional quantum welllayer is formed of In_(x)Ga_(1-x)N, in which x is preferably 0.2 or morein the In-rich region of the two-dimensional quantum well layer. Whenthe two-dimensional quantum well layer has a thickness of 2 nm or more,it is not easy to adjust the emission wavelength into the UV region bythe carrier confinement effect. Therefore, the two-dimensional quantumwell layer has preferably a thickness of 2 nm or less.

Also, according to the present invention, there is provided a nitridesemiconductor light emitting device wherein the additional nitridesemiconductor is made of Al_(y)Ga_(1-y)N (0≦y≦1). Of course, theadditional nitride semiconductor layer may include In.

Also, according to the present invention, there is provided a nitridesemiconductor light emitting device further comprising at least onebarrier layer of Al_(y)Ga_(1-y)N (0≦y≦1) adjacent to the quantum welllayer and having a band gap energy higher than that of the additionalnitride semiconductor layer.

Also, according to the present invention, there is provided a nitridesemiconductor light emitting device wherein the quantum well layer andthe barrier layer of Al_(y)Ga_(1-y)N (0≦y≦1) are alternately laminatedto form a multi-quantum well structure. Preferrably, the pairs of thequantum well and the barrier layer of Al_(y)Ga_(1-y)N (0≦y≦1) is 100pairs or less.

Advantageous Effects

According to the present invention, using the growth interruptionmethod, a thin and high quality In-rich InGaN quantum well layer isgrown. Unlike the conventional UV optical device, in which a Ga-richInGaN quantum well layer is used as an active layer, a thin In-richInGaN quantum well layer with compositional grading is used, whereby itis possible to develop a high efficiency UV light source with a shortwavelength, through the formation of local carrier energy level, carrierconfinement effect and the formation of a single energy level in theenergy band structure.

DESCRIPTION OF DRAWINGS

Further objects and advantages of the invention can be more fullyunderstood from the following detailed description taken in conjunctionwith the accompanying drawings in which:

FIG. 1 is a flow chart for explanation of the method for growing anIn-rich InGaN quantum well layer according to an embodiment of thepresent invention;

FIG. 2 to FIG. 4 are cross-sectional views to show each step of themethod for growing an In-rich InGaN quantum well layer according to anembodiment of the present invention;

FIG. 5 to FIG. 7 are transmission electron microscope photographsshowing the change in layers by growth interruption of In-rich InGaN/GaNquantum well structure according to an embodiment of the presentinvention;

FIG. 8 is a view showing the results of MEIS (Medium Energy IonScattering) measurement and computational simulation to obtain the Incomposition distribution in the InGaN layer of the In-rich InGaN/GaNquantum well structure according to an embodiment of the presentinvention;

FIG. 9 is a view showing the result of PL (Photoluminescence)measurement showing the change of light emission peak at variousthicknesses of the GaN capping layer upon the growth of the In-richInGaN/GaN quantum well structure according to an embodiment of thepresent invention;

FIG. 10 is a view showing energy levels and wave functions in the energyband diagram of the In-rich InGaN/GaN quantum well structure havingcompositional grading to explain the PL result of FIG. 9 according to anembodiment of the present invention, based on the result of FIG. 8;

FIG. 11 is a view showing the calculation result of location of thelight emission peak in the In-rich InGaN/GaN quantum well structure whenthe band gap energy of InN is 0.7 eV and 1.9 eV, based on thecalculation result in the energy band diagram of FIG. 10;

FIG. 12 is a view showing a light emitting device comprising a quantumwell layer structure according to the present invention; and

FIG. 13 is a view showing a light emitting device comprising amulti-quantum wells structure according to the present invention.

MODE FOR INVENTION

Now, the present invention is explained in further detail with referenceto the attached drawings. The following examples may be changed intodifferent forms and the present invention is not limited thereto. Theexamples are given to help those having ordinary knowledge to completelyunderstand the present invention. In the drawings illustrating theembodiments of the present invention, the thicknesses of some layers orregions are magnified for precision of the specification and the samereference numerals indicate the same elements.

FIG. 1 is a flow chart for explanation of the method for growing anIn-rich InGaN quantum well layer according to an embodiment of thepresent invention and FIG. 2 to FIG. 4 are cross-sectional views to showthe respective steps of the method for growing an In-rich InGaN quantumwell layer according to an embodiment of the present invention.

Referring to the step s1 of FIG. 1 and FIG. 2, an In-rich InGaN layer110 is grown on a substrate 105 mounted in a chamber (not shown) at atemperature higher than the growth temperature of a general Ga-richInGaN epitaxial layer by supplying a Group III source for In and anitrogen source.

Since only the Group III source for In and the nitrogen source aresupplied on the GaN substrate 105, it is expected that an InN layer isformed. However, in practice, intermixing of atoms and defect generationoccur in an InN layer having a thickness of 1˜2 ML (monolayer) or moredue to lattice mismatch of 10% or more between GaN an InN. As a result,the In-rich InGaN layer 110 with compositional grading and a high defectdensity is formed.

In this embodiment, the substrate 105 is a GaN substrate comprising aGaN epitaxial layer 102 grown to a thickness of 1μ or more on ahetero-substrate 100, which is made of a different material from GaN, ata high temperature of 1000° C. or more by a conventional 2-step method.Here, the hetero-substrate 100 is for example, a Si, SiC, GaAs orsapphire (Al₂O₃) substrate. However, the In-rich InGaN layer 110 may begrown on a single crystal GaN substrate 102 which is grown by HVPEwithout using the hetero-substrate 100.

In a preferred embodiment, when the In-rich InGaN layer 110 is grownusing a MOCVD (metalorganic chemical vapor deposition) apparatus, thesubstrate 105 is kept at a high temperature of 700° C. to 800° C. Here,since the decomposition of the thin layer may take place due to a highequilibrium vapor pressure of the In-rich InGaN layer 110, a sufficientamount of the Group III source and the nitrogen source are supplied sothat the deposited layer can cover the entire substrate 105. Forexample, the amount of the Group III source and the nitrogen sourceflowing into the chamber is about 10 times of the amount usedconventionally. If TMIn (Trimethylindium) has been conventionallysupplied to the chamber at 30 sccm to grow a bulk InN layer, 300 sccm ofTMIn is supplied according to the present invention. The In-rich InGaNlayer 110 grown using a sufficient amount of the Group III source andthe nitrogen source at a high temperature has a relatively unevensurface and a lot of defects due to the increase of deformation energycaused by the lattice mismatch with the substrate 105. The In-rich InGaNlayer 110 may be grown at 700° C. or less, for example, 650° C. In thiscase, it should be considered that the defect density may be increaseddue to the reduction of atom mobility in the In-rich InGaN layer 110because of the relatively low growth temperature.

Next, referring to the step s2 of FIG. 1 and FIG. 3, growth interruptionto intercept the supply of the Group III source is performed to convertthe In-rich InGaN layer 110 into a two-dimensional nitride semiconductorbuffered layer 110 a with a uniform thickness.

Since the equilibrium vapor pressure of the nitride semiconductor isvery high, during the growth interruption, much decomposition occurs inthe In-rich InGaN layer 110. Particularly, this decomposition phenomenontakes place more vigorously at the protruded region (convex surface) inthe In-rich InGaN layer 110. Through the decomposition, the movementfrom the surface of molecules, and the diffusion in the thin layer, thenitride semiconductor buffered layer 110 a has a reduced thickness andthe surface becomes flat after the growth interruption. Therefore, byproperly controlling the growth interruption time, it is possible toobtain a flat and thin In-rich InGaN layer 110 a having a thickness ofabout 1 nm. The growth interruption time is set in the range of 60seconds or less, depending on the desired thickness. The growthinterruption time may vary according to the growth temperature of theIn-rich InGaN layer 110, and thus, it should not be construed that thepresent invention is limited to the growth interruption time of 60seconds or less. Yet, it should be considered that the defect density inthe thin layer may be increased when the growth interruption time isincreased.

After the growth interruption step, the In-rich InGaN layer 110 a hasthe defects considerably reduced. During the growth interruption, thegrowth interruption temperature is kept at a high temperature equal tothe growth temperature of the In-rich InGaN layer 110. Right after thedeposition, the In-rich InGaN layer 110 having a high defect density anda nonuniform thickness turns to the In-rich InGaN buffered layer 110 ahaving a low defect density and a thickness of about 1 nm by theselective decomposition, the movement from the surface of molecules inprotruded region, and the diffusion in the thin layer during the growthinterruption.

Next, according to the step s3 of FIG. 1, a nitride semiconductorcapping layer 120 is grown on the In-rich InGaN layer 110 a having areduced defect density by the growth interruption at the same or highertemperature for application as an optical device as shown in FIG. 4. Thenitride semiconductor capping layer 120 is grown using a material havinga energy band gap greater than that of the In-rich InGaN layer 110 a. Ina preferred embodiment, GaN, AlN or AlGaN based material is appropriatefor the nitride semiconductor capping layer 120. Here, the nitridesemiconductor capping layer 120 is grown at a temperature equal to thegrowth temperature of the In-rich InGaN layer 110 or at a temperaturehigher than the growth temperature of the In-rich InGaN layer 110 forthe improvement of properties. The thickness may vary from several nm toseveral tens nm, as needed. In order to shift the emission wavelength tothe short wavelength region, a thin barrier layer having a band gapenergy higher than that of the capping layer may be applied on one sideor both sides of the In-rich InGaN layer.

Thus, according to the present invention, by using an In-rich InGaNepitaxial layer having a thickness of about 1 nm as an active layer onthe substrate instead of the conventional Ga-rich InGaN epitaxial layer,it is possible to considerably improve the formation of local carrierenergy level and the carrier confinement effect in the quantum wellstructure. As a result, it is possible to produce an optical device withan improved light emission efficiency.

The present invention is explained in further detail by the followingexperimental examples and the contents which are not described hereinare omitted since those skilled in the art may technically infer them.Also, the following examples do not intend to limit the presentinvention.

The crystal growing method used for forming each thin layer in thisexample was a low-pressure MOCVD with a chamber pressure of 300 Torr anda GaN substrate comprising a GaN epitaxial layer grown to a thickness of2μ on a sapphire substrate was used as a substrate.

As the Group III source and the nitrogen source, TMIn (Trimethylindium),TMGa (Trimethylgallium), ammonia and the like were used and as thecarrier gas, H2 or N2 gas was used.

First of all, the GaN substrate was heated to 1100° C. and kept at thattemperature for 5 minutes to remove surface impurities. Here, ammonia asa nitrogen source was flown, using H₂ gas as a carrier gas, to preventthe decomposition of the GaN epitaxial layer at the high temperature.

Then, the temperature of the substrate was lowered to 730° C. to grow anIn-rich InGaN quantum well layer. After the temperature was lowered to730° C., the carrier gas was changed to N₂ gas and TMIn and ammonia weresupplied to grow an InN layer for 90 seconds. However, the produced InNlayer had nonuniform thickness and defects. Also, due to theatoms-intermixing phenomenon between the InN layer and the GaN substratedisposed below, in practice, not the InN layer but an In-rich InGaNepitaxial layer with compositional grading was formed.

FIG. 5 is a transmission electron microscope photograph taken after anIn-rich InGaN layer with compositional grading was grown at 730° C. anda GaN capping layer having a thickness of 20 nm was formed at the sametemperature. As shown in FIG. 5, when the GaN capping layer 220 wasgrown right after the high temperature In-rich InGaN layer 210 wasformed on the GaN substrate 205 without growth interruption, theproduced high temperature In-rich InGaN layer 210 having a thickness ofabout 2.5 nm showed nonuniformity in thickness and the GaN capping layer220 grown thereon showed a high defect density.

FIG. 6 is a transmission electron microscope photograph taken after theIn-rich InGaN layer which has been grown at 730° C. is subjected to thegrowth interruption for 10 seconds by supplying only ammonia whileintercepting the supply of TMIn and a GaN capping layer is coveredthereon. As shown in FIG. 6, after the growth interruption, thethickness of the In-rich InGaN layer 210 a become uniform to 1 nm andthe GaN capping layer 220 grown thereon showed a remarkably reduceddefect density as compared to the case shown in FIG. 5.

FIG. 7 is a high resolution transmission electron microscope photographtaken after the growth interruption for 10 seconds. As shown in FIG. 6and FIG. 7, by the growth interruption for 10 seconds, the In-rich InGaNlayer 210 a was uniform in thickness and had a smooth interface with theGaN capping layer 220.

Like this, after the flat In-rich InGaN layer with a thickness of 1 nmwas formed through growth and growth interruption at 730° C., the GaNcapping layer was grown to 20 nm at the same temperature for theformation of a single quantum well structure. Meanwhile, a specimen of aGaN capping layer with a thickness of 2 nm was also grown for MEIS(Medium Energy Ion Scattering) study of In composition distribution inthe InGaN layer.

FIG. 8 is a view showing the results of MEIS measurement andcomputational simulation of the In composition distribution in theIn-rich InGaN/GaN quantum well structure having compositional grading,grown as described above. The MEIS method is a non-destructive methodcapable of precisely measuring the composition in a very thin layer atan atom level resolution. The computational simulation was performedusing the ‘SIMPLE’ program which is made by slightly revising theconventional ISAP (Ion Scattering Analysis Program) to examine thecomposition change according to the thickness of the InGaN well layer.

On the MEIS measurement, the specimen of the GaN capping layer grown toa thickness of 2 nm was used to increase sensitivity on the surface. Asa result, it was found that the In-rich InGaN layer having a thicknessof 0.43 nm was present and the In content in this layer was about 60 to70%, which was within the range of 50 to 80% resulted from thetheoretical calculation. Also, it was found that In compositionalgrading was present in the InGaN/GaN interfaces. It was shown by thecomputational simulation, that 0.12 nm InGaN having an In content of 10%was present to the direction of the GaN capping layer, and 0.25 nm InGaNhaving an In content of 30% was present to the direction of the GaNsubstrate. The total thickness of the InGaN layer obtained by the MEISmeasurement was 0.8 nm which agreed with the result of the highresolution electron transmission image in FIG. 7.

FIG. 9 shows photoluminescence (PL) peak spectra resulting from theIn-rich InGaN/GaN quantum well structure having compositional gradingmade by the above-described method, in which PL peak in the near UVregion of about 400 nm was present regardless of the thickness of theGaN capping layer.

This means that the energy level in InGaN/GaN quantum well structure wasnot affected by the change in the thickness of the capping layer. It isbelieved that this is because the high deformation energy caused by thehigh lattice mismatch of 10% or more was relieved by depositing InN onthe GaN substrate.

FIG. 10 shows the energy band diagram in In_(0.6)Ga_(0.4)N/GaN quantumwell structure (GaN/In_(0.1)Ga_(0.9)N (0.12 nm)/In_(0.6)Ga_(0.4)N (0.43nm)/In_(0.3)Ga_(0.7)N (0.25 nm)/GaN) with compositional grading, basedon MEIS result.

Because of difficulty in growth due to, for example, high equilibriumvapor pressure, the properties of InN have not been precisely informed.Recently, some groups that succeeded in growing an InN thin layer byadvancement of growth technology have reported that the band gap energyof InN is not 1.9 eV, as known to the art, but 0.7 eV. However, there isno report on the precise band gap energy of InN. Therefore, consideringboth cases, the light emission peaks in the In_(0.6)Ga_(0.4)N/GaNquantum well structure having compositional grading when the band gapenergy of InN is 0.7 eV and 1.9 eV were calculated.

FIG. 11 shows that the In-rich InGaN/GaN quantum well structure havingcompositional grading can have 400 nm light emission energy. For thiscalculation, the Schroedinger equation was solved using the Fourierseries method calculating energy levels and wave functions in thefrequency space. When the band gap energy of InN was 0.7 eV (1770 nm)and 1.9 eV (653 nm), it was found that by forming the In-rich InGaN/GaNquantum well structure, the emission peak was reduced to 442 nm and 393nm, respectively.

Of course, considering the inaccuracy in values of InN related materialconstants, these data are not absolute but it was proved that theemission in the In-rich InGaN/GaN quantum well structure havingcompositional grading could be observed in the near UV region. Also,since this structure showed only one energy level, a near UV lightsource of a single wavelength could be obtained upon application to anoptical device, regardless of the number of excited carriers.

Also, it was possible to shift the emission wavelength to the shorterwavelength region by forming a thin barrier layer having a band gapenergy higher than that of the capping layer on one side or both sidesof the In-rich InGaN layer. For example, it was found throughcalculation that in case of the Ino.6Gao.4N/GaN quantum well structurehaving compositional grading, the emission wavelength is shifted to 378nm by forming an AlN barrier layer of 3 nm.

Up to now, the present invention is described by the example using theMOCVD method, however, MBE (molecular beam epitaxy) or CBE (chemicalbeam epitaxy) may be used.

Up to now, the preferred embodiment of the present invention has beendescribed. However, it is clear that various modifications can be madewithout departing the scope of the present invention.

FIG. 12 is a view showing a light emitting device comprising a singlequantum well structure according to the present invention. The lightemitting device comprises a substrate 1, a buffer layer 2 grown on thesubstrate 1, an n-type contact layer 3 of Al_(x)Ga_(y)In_(1-x-y)N(0≦x≦1, 0<y≦1, 0<x+y≦1) grown on the buffer layer 2, a quantum welllayer 110 a according to the present invention grown on the n-typecontact layer 3, a capping layer 4 of p-type nitride semiconductor grownon the quantum well layer 110 a, a p-type contact layer 5 ofAl_(x)Ga_(y)In_(1-x-y)N (0≦x≦1, 0<y≦1, 0<x+y≦1) grown on the cappinglayer 4, a light-transmittable electrode layer 6 and a p-type pad 7formed on the p-type contact layer 5, and an n-type electrode 8 formedon the n-type contact layer 3. Here, the capping layer 4 and the p-typecontact layer 5 may be formed of the same material.

FIG. 13 is a view showing a light emitting device comprising amulti-quantum wells structure according to the present invention whichhas a structure comprising the quantum well layer 110 a and the barrierlayer 110 b laminated alternately unlike FIG. 12.

The light emitting device according to the present invention is notlimited to the structures shown in FIG. 12 and FIG. 13. On the basis ofthe quantum well layer 110 a, an Al_(x)Ga_(y)In_(1-x-y)N (0≦x≦1, 0<y≦1,0<x+y≦1) layer disposed under the quantum well layer 110 a and a cappinglayer disposed over the quantum well layer 110 a, the light emittingdevice can be expanded to any light emitting device (such as lightemitting diode and laser diode) with any structure that is clear to theperson in the art.

1. A growth method of nitride semiconductor layer comprising: a firststep for growing a first nitride semiconductor layer on anAl_(χ)Ga_(y)Ini_(-x-)yN (0<x<1, 0<y<1, 0<x+y<1) layer; a second step forreducing the thickness of the first nitride semiconductor layer bygrowth interruption; and a third step for growing a second nitridesemiconductor layer having a band gap energy higher than that of thefirst nitride semiconductor layer on the first nitride semiconductorlayer with the reduced thickness.
 2. The growth method of nitridesemiconductor layer in claim 1, wherein at the first step, an in sourceand a nitrogen source is used for growing the first nitridesemiconductor layer.
 3. The growth method of nitride semiconductor layerin claim 2, wherein an Ga source is further used for the first nitridesemiconductor layer and the amount of the Ga source is very small ascompared to the amount of the In source.
 4. The growth method of nitridesemiconductor layer in claim 3, wherein at the second step, the growthinterruption is performed by supplying the nitrogen source with thesupply of the In source intercepted.
 5. The growth method of nitridesemiconductor layer in claim 2, wherein at the second step, the growthinterruption is performed by supplying the nitrogen source with thesupply of the In source intercepted.
 6. The growth method of nitridesemiconductor layer in claim 1, wherein at the second step, the reducedfirst nitride semiconductor layer has a quantum well structure.
 7. Thegrowth method of nitride semiconductor layer in claim 1, wherein at thefirst step, the first nitride semiconductor layer is grown at atemperature of 700° C. to 800° C.
 8. The growth method of nitridesemiconductor layer in claim 1, wherein the temperature of the firstnitride semiconductor during the growth and the growth interruption ismaintained.
 9. The growth method of nitride semiconductor layer in claim1, wherein at the second step, the growth interruption time is equal toor less than 60 seconds.
 10. The growth method of nitride semiconductorlayer in claim 1, wherein the second nitride semiconductor layer ifgrown at a temperature equal to or higher than that of the first nitridesemiconductor layer.
 11. A nitride semiconductor light emitting devicecomprising: a substrate; at least one nitride semiconductor layer grownon the substrate and including an top layer of Al_(x)Gayini_(-x-)yN(0≦x≦1, 0<y≦1, 0<x+y<1); a quantum well layer grown on the top layer ofAl_(x)Ga_(y)in_(1-x-)yN (0<x<1, 0<y<1, 0<x+y<1); and, an additionalnitride semiconductor layer grown on the quantum well layer and having aband gap energy higher than that of the quantum well layer; wherein thequantum well layer comprises an In-rich region, a first compositionalgrading region with In content increasing between the top layer ofAl_(x)Ga_(y)Ini_(-x-y)N (0≦x≦1, 0<y≦1, 0<x+y≦1) and the In-rich region,and a second compositional grading region with In content decreasingbetween the In-rich region and the additional nitride semiconductorlayer.
 12. The nitride semiconductor light emitting device in claim 11,wherein the quantum well layer is formed of In_(x)Gai_(-x)N and x in theIn-rich region of the quantum well layer is equal to or more than 0.6.13. The nitride semiconductor light emitting device in claim 11, whereinthe quantum well layer is grown using an In source and a nitrogensource, and the thickness of the quantum well is reduced by growthinterruption which is performed by supplying the nitrogen source withthe supply of the In source intercepted.
 14. The nitride semiconductorlight emitting device in claim 11, wherein the quantum well layer isformed of In_(x)Gai_(-x)N and x in the In-rich region of the quantumwell layer is within a range of 0.5 to 0.8.
 15. The nitridesemiconductor light emitting device in claim 11, wherein the thicknessof the quantum well is equal to or less than 2 nm.
 16. The nitridesemiconductor light emitting device in claim 15, wherein the quantumwell layer is formed of In_(x)Gai_(-x)N and x in the In-rich region ofthe quantum well layer is equal to or more than 0.2.
 17. The nitridesemiconductor light emitting device in claim 11, wherein the additionalnitride semiconductor is formed of Al_(y)Gai_(-y)N (O≦y≦1).
 18. Thenitride semiconductor light emitting device in claim 11, furthercomprising at least one barrier layer of Al_(y)Gai_(-y)N (0≦y≦1)adjacent to the quantum well layer and having a band gap energy higherthan that of the additional nitride semiconductor layer.
 19. The nitridesemiconductor light emitting device in claim 18, wherein the at leastone barrier layer of Al_(y)Gai-_(y)N (0≦y≦1) has a thickness equal to orless than 5 nm.
 20. The nitride semiconductor light emitting device inclaim 18, wherein the quantum well layer and the at least barrier layerof Al_(y)Ga1-yN (0≦y≦1) are alternately laminated to form amulti-quantum well structure.
 21. The nitride semiconductor lightemitting device in claim 20, wherein the pairs of the quantum well andthe at least barrier layer of Al_(y)Ga1-yN (O≦y≦1) are equal to or lessthan 100 pairs.
 22. The nitride semiconductor light emitting device inclaim 11, wherein the top layer of Al_(x)Ga_(y)Ini-χ_(y)N (0<x<1, 0<y<1,0<x+y<1) is GaN.
 23. The nitride semiconductor light emitting device inclaim 12, x in the In-rich region of the quantum well layer is equal toor less than 0.7.